On the Localized Nature of the Structural Transformations of Li2MnO3 Following Electrochemical Cycling. Issue 23 (28th September 2015)

• Record Type: Journal Article
• Authors: Phillips, Patrick J.; Bareño, Javier; Li, Yan; Abraham, Daniel P.; Klie, Robert F.
• Is Part Of: Advanced energy materials. Volume 5:Issue 23(2015:Dec.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2015-09-28
• Subjects: annular bight field imaging -- atomic‐resolution scanning transmission electron microscopy -- Li‐ion batteries -- spinels -- synchrotron X‐ray dirffraction; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201501252
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract : Although the Li‐excess layered‐oxide Li2 MnO3 has a high theoretical capacity, structural transformations within the oxide during electrochemical cycling lead to relatively low experimental capacities, hindering its use in practical applications. Here, aberration‐corrected scanning transmission electron microscopy/electron energy loss spectroscopy and high‐resolution X‐ray diffraction are used to characterize the oxide following electrochemical cycling. Microscopy reveals the coexistence of regions with local monoclinic, spinel, and rock‐salt symmetries, indicating localized and inhomogeneous structural evolutions. Crystal structure transformations are observed both at the particle surface and in the bulk. At the surface, these transformed regions resemble spinel Mn3 O4 or rock‐salt MnO, consistent with oxygen loss. In the bulk, the regions resemble defect spinels, such as the layered‐spinel Li x Mn4/3 O4, which suggest a partial phase transformation consistent with oxygen retention. Both microscopy and diffraction data of the cycled sample indicate areas of pristine Li2 MnO3 ; the presence of such areas, in close proximity to Li x Mn4/3 O4 areas, suggests that the layered to spinel structure transformation is partially reversible. Spinel, disordered rock salt, and pristine areas are also observed in Li2 MnO3 samples intentionally damaged by electron beam irradiation. This observation indicates that the dynamic processes resulting in phase transformations can be studied for a variety of oxide systems by a judicious selection of irradiation conditions. Abstract : The localized structural and electronic transformations of Li2 MnO3 following electrochemical cycling are presented in detail and at the atomic scale through scanning transmission electron microscopy and high‐resolution X‐ray diffraction analysis. Transformations are shown to exist in the bulk and at the surface, resulting in regions with defect spinel‐Li x Mn4/3 O4, spinel‐Mn3 O4, and rock‐salt MnO symmetry.